Water management device for gas chromatography sample concentration

ABSTRACT

A water management system removes water vapor from the analyte slug that is desorbed from the trap. The water management system includes a device having a passage through which the volatile organic chemicals and water pass, the passage being designed to remove water vapor by swirling action on the stream. The amount of water removed is more than can be accounted for by simple condensation. The invention also includes the adjustment of the temperature of the water management device during the sample concentration cycle to prevent undesired condensation prior to desorption.

This is a continuation of application Ser. No. 08/282,171, filed Jul.29, 1994, now U.S. Pat. No. 5,470,380; which was a division ofapplication Ser. No. 08/061,986, filed May 14, 1993, now U.S. Pat. No.5,358,557; which was a divisional of application Ser. No. 07/848,395,filed Mar. 9, 1992, now U.S. Pat. No. 5,250,093.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to sample concentration foranalyzing volatile organic compounds in air, water and soils. Moreparticularly, the invention involves a device for removing water vaporfrom the analyte slug as it is carried from the trap of the sampleconcentrator to the gas chromatographic column.

2. Related Art

Sample concentrators are used in purge-and-trap, headspace, and thermaldesorption gas chromatography ("GC") analysis. Purge-and-trap GCtechnique has been used for analyzing volatile organics in water sinceapproximately the early 1970's . In 1987 the U.S. EnvironmentalProtection Agency ("EPA") promulgated national primary drinking waterregulations for certain volatile organic chemicals ("VOCs"). The EPAalso proposed maximum contamination levels for eight volatile organicchemicals. These regulations require the use of the purge-and-trap GCtechnique. In addition to the eight regulated volatile organicchemicals, the EPA also promulgated monitoring requirements for anadditional 52 synthetic volatile organic chemicals.

The EPA has approved certain analytical methods for analyzing these 60compounds. One of the methods is 502.2, a purge-and-trapcapillary-column GC method using a photoionization detector and anelectrolytic conductivity detector joined in series. A second method ismethod 524.2, a purge-and-trap capillary-column GC-MS method.

Purge-and-trap systems for analyzing VOCs in drinking water have beenassembled from a variety of equipment typically including a purgingdevice, trap, and desorber. These systems also are referred to as sampleconcentrators. The purge-and-trap system or sample concentratorinterfaces to a GC capillary column, then with a photoionizationdetector/electrolytic conductivity detector or a mass-spectrometer.These components are interconnected via pneumatic conduits.

Highly volatile organic compounds with low water solubility areextracted (purged) from the sample matrix by bubbling an inert gas(i.e., helium or nitrogen) through a five milliliter aqueous sample.Purged sample components are trapped in a tube containing suitablesorbent materials. When purging is complete, the sorbent tube is heatedand backflushed with the inert gas to desorb trapped sample componentsonto a capillary GC column. The column is temperature programmed toseparate the method analytes which are then detected with aphotoionization detector (PID) and a halogen specific detector placed inseries, or with a mass spectrometer.

Tentative identifications are confirmed by analyzing standards under thesame conditions used for samples, and comparing results and GC retentiontimes. Additional confirmatory information can be gained by comparingthe relative response from the two detectors. Each identified componentis measured by relating the response produced for that compound to theresponse produced by a compound that is used as an internal standard.For absolute confirmation, the gas chromatography/mass spectrometry(GC/MS) determination according to method 524.1 or method 524.2 may beused.

As stated above, the typical purge and trap system consists of thepurging device, trap, and desorber. Systems are commercially availablefrom several sources that meet EPA specifications.

Under EPA specifications, the glass purging device must be designed toaccept five to twenty-five ml. samples with a water column at least 5cm. deep. Gaseous volumes above the sample are kept to a minimum toreduce "dead volume" effects. The purged gas passes through the watercolumn as finely divided bubbles.

The sorbent trap is a tube typically at least 25 cm. long and having aninside diameter of at least 0.105 inches. The trap contains certainsorbent materials which the EPA has specified as 2,6-diphenylene oxidepolymer, silica gel, and coconut charcoal. The EPA regulations specifythe ratios of the adsorbent material. The desorber must be capable ofrapidly heating the trap to 180° C.

The model 4460A sample concentrator manufactured by 0I Analytical ofCollege Station, Tex., is an example of a purge and trap, or sampleconcentrator, device. The model 4460A is a microprocessor controlleddevice that stores method 502.2 and 524.2 operating conditions asdefault parameters. Operating conditions may be changed by the user toaccommodate other types of purge and trap analysis.

In addition to purge-and-trap methods and analyses, sample concentrationgas chromatography is used in headspace analysis of liquids and solids,and in thermal desorption analysis of air tube samples. Headspace andthermal desorption techniques are not only used for environmentalanalyses, but also for clinical and industrial applications.

During all sample concentration GC analysis, some amount of water ispurged from the sample and caught in the trap along with the compoundsof interest. This is a problem encountered in the prior art. A typicalrate of water transfer is 1 microliter per minute of purge time. Withoutany water management system, during the 11-minute purge time required bymethod 502.2, approximately 10 to 11 microliters of water aretransferred to the trap. This water transfer as a function of time isrepresented in FIG. 9. When the trap is heated, the VOCs and the watervapor are desorbed into the GC column. The presence of water vapor inthe capillary column has many detrimental effects including shifts ofanalyte retention times, the quenching of PID response, deterioration ofthe nickel reaction time in the ELCD, and the suppression ofquantification ion response in a mass spectrometer. Along with trappedwater, there also may be trapped methanol causing deleterious effects onthe separation and detection of VOCs.

FIGS. 1 and 2 are examples of plots showing how water transfer affectsion response of a GC or mass spectrometer ("MS"). The units on thehorizontal axis are minutes of GC run time, and the units on thevertical axis are indicative of the abundance of each analyte.

FIG. 1 represents a GC or MS response sensitive to water as well as theanalytes of interest. Water transfer during approximately the first sixor seven minutes is represented on this plot as a "plateau" during thatperiod. Thus, detection of analytes is difficult during that period.

FIG. 2 represents the same analysis as that of FIG. 1, except the GC orMS is sensitive only to an ion range excluding water. Despite theabsence of the plateau from FIG. 1, water transfer during approximatelythe first six or seven minutes tends to diminish or obscure the peaks ofinterest during that period. Typically, peaks are lower due to thepresence of water vapor. Therefore, the plot of FIG. 2 similarlypresents analyte detection problems because of the water transferproblem.

Typically, the methods described above call for a 4 minute desorbperiod, which is represented on the GC or MS plot as the first 4 minutesof run time. Generally, few if any analytes show up on the GC or MSduring approximately the first 4 minutes. However, methane and waterbegin appearing during that period. After the four minute desorb period,water continues to appear, obscuring the analytes of interest.

Water continues to be transferred from the trap to the GC during theremainder of the run time, or will be limited to approximately the first6 or 7 minutes of run time, depending on various factors. In general, ifwater transfer time is reduced, there greater distortion of results(represented graphically as a "higher" plateau) during that reduced timeperiod. If the water transfer time is extended, the distortion willcontinue further during the GC run time. Regardless of the length oftime during which water transfer occurs, it has a tendency to obscurethe analytes of interest.

Devices in the prior art addressing the water transfer problem haveinvolved placing a condenser in line between the trap and GC. However,removing water vapor by condensation has certain disadvantages. Onedisadvantage is "dead volume," which has deleterious effects on the GCanalysis. Due to dead volume, volatile compounds are trapped in thecondenser, and GC peaks exhibit "tailing."

Another disadvantage of the condensation approach is that passing of thecompound through a cold zone in the condenser interrupts the desiredflow of the compound to the GC column. Retention times for analytes areless predictable and repeatable, and a fraction of the analyte may beretarded in the cold zone, reducing the ability to detect and quantifycertain compounds. Further, it is desirable to heat the pneumatic linesso that condensation does not occur.

In the OI Analytical model 4460A sample concentrator, the desorption ofwater vapor onto the GC column is reduced by a water management systemthat utilizes rapid trap heating at 800° C. per minute coupled with anexpansion/condensation chamber that allows only 0.25 microliters perminute of water vapor to desorb onto the GC column. Due to this watermanagement system, over 90% of the trapped water can be rejected. Whenthe chamber is at 35 degrees C., approximately 1.1 microliters of watervapor are desorbed onto the GC column during the 4 minute desorb period.The GC response to water vapor only as a function of time is shown ifFIG. 9. The same device at 25 degrees C. delivers approximately 0.93microliters of water to the GC column. This feature is particularlyvaluable in detection and measurement of some early eluting compoundswhose PID, ELCD or MS responses are normally attenuated by transfer ofwater vapor to the detector. These systems also reduce water-activateddeterioration of the ELCD nickel reaction tube and the subsequent lossof response to certain compounds.

Another example of a condensor-type device is the TEKMAR 2000 Plus purgeand trap concentrator, with a moisture control module ("MCM"). The MCMcondensate trap cools the VOCs and water that pass through, thenpreheats the sorbent trap. Upon reaching the preheat temperature, thetrap is backflushed with carrier gas sweeping the volatiles and waterfrom the heated trap over to the cooled MCM condensate trap. The watercondensed from the gas stream is isolated from the carrier gas flowpath, and then is heated to vaporize through a vent. A thermoelectricmodule (Peltier effect module) is used to cool and heat the MCM in aneffort to remove the water vapor from the analyte stream. The Peltiereffect module passes electric current through the junction of twothermoelectric materials to cool the MCM, and then to subsequently heatit to remove the water vapor. However, the Peltier module is susceptibleto failure after repeated heating and cooling cycles. In addition, thecost of the MCM unit and the electrical requirements are disadvantagesof such a water management system.

As another alternative to eliminate water vapor transfer to the GCcolumn, OI Analytical's Anhydrator reduces water transfer to the GCcolumn to less than 0.004 microliters per minute. The Anhydratorconsists of Nafion tubing available from Perma-Ture Corporation. TheAnydrator has disadvantages and problems including the irreversible lossof polar analytes such as acetone and methanol, which ar removed alongwith the water.

SUMMARY OF THE INVENTION

The present invention overcomes the above-mentioned problems anddisadvantages by providing a water management system wherein the amountof water vapor removed is greater than what can be accomplished by vaporpressure and temperature behavior. The amount of water removed is morethan can be accounted for by simple condensation.

The invention includes a water management device having a passagethrough which VOCs and water vapor pass, the passage designed to removewater vapor by swirling action on the stream. The passage has additionalsurface area, such as an internally threaded configuration, withoutsignificantly increasing the dead volume, and without temperatures aslow as the prior art.

The invention also includes a process of adjusting the temperature ofthe water management device during the purge, desorb, and bake cycle.During the purge step, the device reaches a temperature somewhat higherthan the trap temperature, to reduce condensation before the analytestream reaches the trap. Just prior to desorb, the water managementdevice is cooled further, approaching ambient room temperature, toremove water vapor from the analyte stream being desorbed from the trapto the GC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical GC or MS response sensitive to water and theanalytes of interest, showing the detrimental effect of water transferwithout the present invention.

FIG. 2 is a typical GC or MS response sensitive only to an ion rangeexcluding water, showing the detrimental effect of water transferwithout the present invention.

FIG. 3 is a side view, partially in section, of the water managementdevice according to the present invention.

FIG. 4 is a top view, in section, of the water management device shownin FIG. 3.

FIG. 5 is a section view taken along section line 5 of FIG. 3, showingthe neck between the first and second sections of the bore in the watermanagement device.

FIG. 6 is a perspective view, in section of the water management deviceof the present invention.

FIG. 7 is a schematic diagram of the water management device of thepresent invention and the other components used in a typical sampleconcentration/GC system.

FIG. 8 is a plot of the temperature of the water management device ofthe present invention as a function of time.

FIGS. 9A, 9B, and 9C are typical GC or MS response sensitive only towater, for volume of water transfer as a function of time, comparingwater transfer to the GC without any water management system, with theOI Analytical Model 4460A, and with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In a preferred embodiment, water management device 10 may be interposedin the pneumatic line between the trap 11 and GC 12, as shown in FIG. 7.Also shown in FIG. 7 is a sparge vessel 13, vent 14, and pneumatictubing 15 connecting the components.

Typically, the sample concentration cycle involves the steps of purge,desorb, and bake. During purge, the analyte stream flows from spargevessel 13 through water management device 10 to trap 11, which is at acool temperature (approximately 20 degrees C.). During desorb, the trapis heated (to approximately 180 degrees C.) and backflushed with carriergas. The analyte stream flows from the trap to the water managementdevice and then to the GC or MS. During bake, both the trap and thewater management device are heated (to approximately 240 degrees C.).Dry gas is introduced to the system to move water vapor out of the watermanagement device and trap through vent 14.

Although a preferred embodiment s invention is intended for desorb byback-flush of the trap 11, it is contemplated that the invention mayalso be used with a fore-flush of the trap.

Now referring to FIGS. 3-6, a preferred embodiment of the watermanagement device 10 is shown. In this embodiment, the inventioncomprises a stainless steel body portion 20 preferably having anL-shaped configuration. The body portion is gold plated. A passage orbore 31 extends through the body 20, from a first end 32 to a second end33. The bore 31 has a first section 34 adjacent the first end, and asecond section 35 adjacent the second end. The first and second sectionsof the bore meet at intersection 16, preferably at an angle ofapproximately ninety degrees.

As stated above, the present invention is primarily intended for usewith a back-flush system, but also may be used with a fore-flush system.When used in a back-flush system, the first end of the device is theoutlet during purge and the inlet during desorb, and the second end isthe inlet during purge and the outlet during desorb. The removal ofwater is intended to take place primarily during the desorb step, whichwill be discussed below.

In desorb, the analyte stream from the trap 11 enters the first section34 of the bore, which has a stepped diameter and a total length ofapproximately 1.000 inches. Starting from the first end 32, the firstsection 34 of the bore is internally threaded at 41 to provide a fittingbody for engagement with a nut (not shown) and pneumatic tubing, whichis then connected to trap 11. Adjacent the first end, a portion of theinternally threaded portion 41 has a conical shape 42 for mating with aferrule (not shown) on the pneumatic tubing. Instead, external threadsmay be used if desired.

Still referring to first section 34 of the bore, in a preferredembodiment threads 41 terminate at 43, and the bore has an internaldiameter of 0.125 inches. This internal diameter can be varied dependingon various factors such as the flow rate desired, the pneumatic tubingand the trap used in the system, and the inner diameter of the GC columnused. This diameter is preferred for use with pneumatic tubing having aninternal diameter of 0.03 inches, a trap having an internal diameter of0.105 inches, and GC column internal diameters ranging fromapproximately 0.010 to 0.020 inches.

In a preferred embodiment shown in FIGS. 3-6, the first section 34includes internal shoulder 44 and a reduction in the bore to 0.080inches, as shown at neck 45. The reduction in diameter from 0.125 to0.080 tends to increase the velocity of the analyte stream flowingthrough the bore. The neck 45 has an axial length of 0.10 inches andintersects the second section 35 of the bore at intersection 16.

In a preferred embodiment the first and second sections of the boreintersect at an angle of ninety degrees. As shown in FIG. 5, the neck 45is off-center from the center line of the first section of the bore, andis similarly off-center from the second section of the bore, as will beexplained in more detail below.

The second section 35 of the bore has an internal diameter of 0.110inches. The second section forms a T with the first section, with theone leg extending down to reservoir 48. Water vapor that is caught inthe second portion of the bore drains downwardly into the reservoir 48and remains there until the bake step in the cycle. Thus, the watermanagement device should be aligned such that water will drain into thereservoir. Preferably, the second section of the bore is verticallyaligned.

The reservoir is considered "unswept volume" or "dead volume" in thesystem, as the analyte stream will normally bypass that volume. Thereservoir 48 has an axial length of about 0.280 inches and a volume ofapproximately 40 to 50 microliters. The volume of the reservoir may bevaried depending on the maximum volume of water that will be removedfrom the analyte stream as it passes through the second section of thebore. However, it is contemplated that the reservoir volume should notbe significantly below about 10 microliters because it would beinsufficient for the anticipated water volume, or above about 100microliters because of deleterious effects of "unswept volume" or "deadvolume" on the system.

The second section 35 also is configured such that the "dead volume" isminimized. An internal diameter of 0.110 inches is most preferred forsecond section 35, which is primarily intended for use with GC columnshaving internal diameters of between approximately 0.010 and 0.020inches. It is contemplated that the internal diameter of the secondsection should be no greater than approximately 11 times the internaldiameter of the GC column.

In a preferred embodiment, the second section of the bore is internallythreaded. This geometry results in a swirling effect on the analyte slugas it leaves the first section and enters the second section, to removemore water vapor from the analyte slug than would be expected at a giventemperature and pressure. Preferably, the length of the internallythreaded portion 49 is 1.080 inches. It is contemplated that the lengthof this portion will be approximately ten times the diameter of thesecond section.

Although a threaded configuration is shown for the second section, othernon-smooth geometries may be used to remove water vapor and cause thatwater vapor to be trapped in the second section of the bore. Forexample, a series of ridges may be included in the interior surface ofthe second section. Alternatively, the second section of the bore may beconical in configuration. As with the threaded or ridged configuration,the conical shape causes a swirling effect on the water vapor to removethat vapor from the analyte slug.

As discussed above, the neck 45 is off-center from the second section 35of the bore. This can be seen in FIG. 5. This arrangement enhances theswirling effect because of a tangential feed to the second section ofthe bore. Further, the neck's internal diameter is smaller than thediameter of the second section of the bore. Thus, the analyte streamloses heat due to expansion upon entering the second section of thebore.

The second section of the bore has a total length of preferably about1.600 inches. Adjacent the second end is a conical portion 50 forengagement with a ferrule or other connection (not shown). Also shownadjacent the second end are external threads 51 for engagement with afitting and pneumatic tubing, which is then connected to GC 12 and vent14.

As discussed above, water vapor that is removed from the analyte slugdrains into reservoir 48 and accumulates therein. During the bake step,the water in reservoir 48 may be removed.

The configuration of the water management device is such that the amountof water vapor removed is above what one would expect to be accomplishedfrom condensation. A number of different geometries for the secondsection are contemplated, including those having an irregular shapedsurface or noncylindrical shape. In contrast, the prior art hasgenerally specified that the pneumatic tubing and passageways betweenthe trap and GC are smooth-walled.

In the prior art, i.e. the OI Analytical Model 4460A, at 35 degrees C.approximately 1.1 microliters of water vapor are desorbed onto the GCcolumn during the 4 minute desorb period. Because of normalcondensation, only approximately 0.93 microliters of water would bedelivered to the GC column if the temperature was reduced to 25 degreesC. However, at the same temperature of 25 degrees C., the presentinvention reduces the amount of water delivered to the GC column muchfurther, to approximately 0.25 microliters. Thus, the present inventionsubstantially reduces the amount of water transfer at a giventemperature.

The water management device of the present invention includes a pair ofbores 61,62 adjacent the second section. Bore 61 is for insertion of aheating cartridge (not shown), which is preferably of between 50 and 100watts. Bore 62 is for a thermocouple (not shown), preferably a Type K.The heating cartridge and thermocouple are functionally connected to anelectrical power source (not shown) for heating the water managementdevice, and monitoring its temperature. The heating cartridge andthermocouple are anchored to the water management device body with setscrew 80.

Also shown in FIG. 6 is a heat sink 70 attached to the water managementdevice to direct heat away from the device. Not shown is an electric fanwhich is configured to blow air on the water management device forcooling of the device as will be described in more detail below.Although a fan is used in the preferred embodiment, a variety ofconventional cooling apparatus may be used for this purpose.

The operation of the water management device during a typical sampleconcentration cycle will be described below. This process ismicroprocessor controlled with certain parameters that may be selectedby the operator.

As shown in FIG. 8, the sample concentration cycle includes the purge,desorb and bake steps. Typically, the purge step is 11 minutes, thedesorb step is 4 minutes, and the bake step is at least 7 minutes. Thevertical axis of FIG. 8 is the temperature of the water managementdevice and sorbent trap in degrees C.

During the bake step, the water management device and trap are heated toan operator-selected temperature, preferably approximately 240 degreesC. In a preferred embodiment, the heating means for the water managementdevice is the heating cartridge inserted in bore 61. The bake stepserves to expel water vapor out of the system. During this step, bakegas may be introduced to flow through the trap and water managementdevice, and out through vent 14.

Once the bake temperature has been reached, or following anoperator-selected time period, the microprocessor activates a fan (notshown) to begin cooling the trap and the water management device. Themass of the water management device is larger than that of the trap, soit cools at a much slower rate.

Once the desired temperature is reached in the trap, preferably about 25degrees C. or ambient temperature, as selected by the operator, thepurge step begins. During this time, the water management device iscooled and/or heated to maintain its temperature at approximately 20degrees higher than the temperature of the sample in the sparge vessel.Therefore, if the water sample is at 20 degrees C., the water managementdevice is at 40 degrees C. To maintain the water management device atthis temperature during the purge step, the heating cartridge and or fanare activated as needed by microprocessor control.

There is a significant advantage achieved with the water managementdevice at a higher temperature than the trap during purge. During thepurge step, it is intended that no condensation or other removal ofwater vapor from the analyte stream should occur. The higher temperatureof the water management device prevents condensation from taking placebefore the analyte stream reaches the trap. If condensation occurredbefore reaching the trap, it is likely that condensed water vapor wouldremain in the water management device until the desorb step, when thewater vapor and/or droplets would flow directly to the GC as the systemis backflushed. Therefore, maintaining a higher temperature of the watermanagement device during purge reduces the amount of water vapor thatenters the GC, thereby improving detection of analytes.

As stated above, the purge step is typically about 4 minutes. Beginningin the last minute of purge, or at some other operator-selected time,the fan is activated to further cool the water management device. Thisis done to prepare the water management device for the desorb step whichdirectly follows. During this final minute of purge, the watermanagement device is cooled to (a) a selected temperature, or (b) atemperature at which the device stabilizes for a selected period oftime, such as 20 seconds. The operator may select either of theseparameters and temperatures. The temperature of the water managementdevice tends to stabilize after approximately one minute, as furthercooling of the water management device below ambient is extremely slowand difficult to achiever with only the fan as the cooling device.Therefore, if the selected temperature is not reached at the end of theselected time period, option (b) is the default parameter. At the end ofpurge, the desorb step does not begin until the selected temperature hasbeen reached or the temperature of the water management device hasstabilized for the selected time period.

When the water management device reaches the selected temperature, ormaintains a stabilized temperature for the selected time period, thedesorb step begins. In desorb, the trap is heated to a temperature ofapproximately 180 degrees C. by running electric current through thetrap. The trap back-flushed with carrier gas to remove the trappedanalytes. The analyte slug then flows to the water management device onits way to the GC. While the trap is at 180 degrees C., the fan coolsthe water management device to ambient or another selected temperaturewhich is generally slightly greater than ambient. Preferably, a shortlength of stainless steel tubing acts as a temperature buffer betweenthe trap and the water management device. During desorb, the watermanagement device removes water vapor from the analyte slug. At the endof the desorb step, the bake step repeats.

As shown in FIG. 9, under EPA Method 524.2 operating conditions theamount of water transfer to the GC with the present invention issubstantially below that of the prior art. Without any water managementsystem, the volume of water transfer to the GC is typically 11 mg. Withthe condensation approach of the OI Analytical Model 4460A, the volumeof water transfer is approximately 1.1 mg. The present invention reducesthe water transfer volume to only 0.25 mg.

One advantage of the present invention is that it allows a wider varietyof sample temperature ranges. For example, the sample temperature can befrom 0° to 100° C., whereas other means of water management did not workwell above 30° C. Further, the water management device does not requirecooling apparatus to bring its temperature below ambient roomtemperature. Since the water management device and sample are not cooledbelow ambient, the invention helps to reduce the "tailing" of the GCpeaks caused by reduced temperature of prior art water managementsystems.

Another advantage of the present invention is that it reduces the "deadvolume" that was present in prior art condensation devices used forwater vapor removal. The reduction of "dead volume" enhances GCdetection and analysis.

Another advantage to the present invention is that water vapor may beremoved from the analyte slug without expensive and complex mechanicalor electromechanical mechanisms that are subject to failure afterrepeated cycling.

Although variations in the embodiment of the present invention may noteach realize all the advantages of the invention, certain features maybecome more important than others in various applications of the device.The invention, accordingly, should be understood to be limited only bythe scope of the appended claims.

What is claimed is:
 1. An apparatus for removal of water from analytesbeing purged from a sparge vessel to a trap and desorbed from the trapto an analytical instrument, comprising:(a) purge means for purging theanalytes from the sparge vessel and passing the purged analytes througha passage connecting the sparge vessel to the trap; (b) desorbing meansfor desorbing the analytes from the trap and passing the desorbedanalytes through the passage from the trap to the analytical instrument,the passage being configured to impart an angular velocity on theanalytes flowing from the trap to the analytical instrument; and (c)heating and venting means for heating the passage to a temperaturesufficient to expel water vapor from the passage through a vent.
 2. Theapparatus of claim 1 wherein the passage imparts angular velocity on theanalyte stream by causing the analyte stream to flow in a helical paththrough the passage during use of the desorbing means.
 3. The apparatusof claim 1 wherein the passage imparts angular velocity on the analytestream by causing the analyte stream to flow in a cylindrical paththrough the passage during use of the desorbing means.
 4. The apparatusof claim 1 wherein the passage is thermally isolated from the trap. 5.The apparatus of claim 1 further comprising a fan for cooling thepassage.
 6. The apparatus of claim 1 further comprising means forflowing the analytes through the passage in opposite directions duringpurging and desorption.
 7. The apparatus of claim 1 wherein the passageis constructed to retain enough heat during purging to substantiallyprevent condensation of water in the passage.
 8. The apparatus of claim1 wherein a heating cartridge and thermocouple are used for heating thepassage.
 9. The apparatus of claim 1 wherein said passage impartsangular velocity on the analyte stream by spiraling the analyte streamduring use of the desorbing means.
 10. An apparatus for removal ofexcess water from analytes being purged from a sparge vessel onto a trapand desorbed from the trap to an analytical instrument, comprising:(a)purging means for purging wherein the analytes flow from the spargevessel through an L-shaped passage to the trap, the L-shaped passagebeing connected to a vent; (b) desorbing means for desorbing wherein theL-shaped passage is configured to impart an angular velocity on theanalyte slug as it flows from the trap to the analytical instrument; and(c) heating means for heating the L-shaped passage to a temperaturesufficient to vaporize water in the L-shaped passage and to expel thevapor from the vent.
 11. The apparatus of claim 10 further comprisingmeans for maintaining the temperature in the passage at a temperature atleast as high as ambient room temperature during use of the desorbingmeans.
 12. The apparatus of claim 10 further comprising means formaintaining the temperature in the passage at a temperature near ambientroom temperature during use of the desorbing means.
 13. The apparatus ofclaim 10 further comprising means for maintaining the temperature in thepassage at a temperature higher than the temperature of the sample inthe sparge vessel during use of the purging means.
 14. The apparatus ofclaim 10 further comprising means for maintaining the temperature in thepassage at a temperature sufficiently high to prevent condensation ofwater in the L-shaped passage before reaching the trap during thepurging step.
 15. The apparatus of claim 10 wherein the heating meansfurther comprises means for flowing a gas through the L-shaped passageand out through the vent.
 16. The apparatus of claim 10 wherein theheating means further comprises means for expelling excess water outthrough the vent.
 17. The apparatus of claim 10 wherein the L-shapedpassage further comprises a reservoir for drainage of excess waterremoved from the analyte stream.
 18. The apparatus of claim 10 whereinat least a portion of the L-shaped passage has a non-smooth internalsurface.
 19. The apparatus of claim 10 wherein the L-shaped passage isgold-plated.
 20. The apparatus of claim 10 wherein the L-shaped passageis configured to increase the velocity of the analyte stream flowingthrough the L-shaped passage during use of the desorbing means.
 21. Theapparatus of claim 10 wherein a portion of the L-shaped passage has anarrowed diameter configured to increase the velocity of the analytestream flowing through the L-shaped passage during the use of thedesorbing means.
 22. The apparatus of claim 10 further comprising a fanto cool the L-shaped passage.
 23. The apparatus of claim 10 wherein atleast a portion of the L-shaped passage causes swirling of the analytesand water flowing through the passage during the use of the desorbingmeans.
 24. The apparatus of claim 10 wherein the L-shaped passageimparts a circular motion on the analytes and water flowing through thepassage during the use of the desorbing means.